The studies described in this proposal are designed to test the hypothesis that the surrounding endocrine milieu exerts an effect upon the "type" of FSH and LH that is present within and is secreted from the anterior pituitary gland of the golden hamster. To test this hypothesis, we will examine a variety of physiological conditions in which dramatic alterations in the biosynthesis and secretion of pituitary gonadotropins have been observed. Hamsters will be killed at specific times throughout the estrous cycle, following phenobarbital treatment, following castration and subsequent hormone replacement, during states of hyperprolactinemia and specific photoperiodic regimens known to influence the reproductive neuroendocrine system. Serum samples obtained from each animal within each experimental group will be assessed for estradiol, progesterone or testosterone concentration by radioimmunoassay (RIA). Serum LH and FSH will be measured by RIA and in vitro bioassay. Pituitary tissue from each animal will be hemisected. Half will be assessed for HL and FSH content by RIA and bioassay. The remaining half will be placed in an organ culture system and exposed to pulses of LHRH or potassium ions. Secretory responses of LH and FSH will be quantiated by RIA and bioassay. Significant effort will be expended to improve the sensitivity and specificity of a FSH in vitro bioassay. Whenever differences between control and treated pituitary or medium samples are observed by RIA and bioassay, those samples will be analyzed by a column isoelectric focusing technique. In this way, differences in FSH bioactivity will be correlated with the relative proportion of FSH forms in that sample as well as the complete reproductive endocrine status of each pituitary donor. The results of these studies will provide us with an understanding of the physiological significance of hormone heterogeneity and an understanding of the responses of this unique neuroendocrine mechanism during a variety of physiologic states. This information is critical to our comprehension of the mechanisms by which reproductive organs communicate.